Described herein are particles, preferably toner particles comprised of at least binder and colorant, having a doped conductive polymer material as a surface additive on the external surface of the particle. The presence of the external doped conductive polymer material enables the particles to retain a substantially uniform charge distribution over the surface of the particles over time, and also enables appropriate control over the triboelectric (tribo) properties of a developer. Also described are developers comprised of such particles in admixture with carrier particles, and methods of making the particles and developers.
It is desirable for toner particles to exhibit a substantially uniform charge distribution over the surface of the toner particles. A freshly made toner typically exhibits a substantially uniform charge distribution, probably because the external additives on the toner particle surface are able to move sufficiently on the toner particle surface to permit the charge to be evenly distributed over the surface of the toner particle. However, it has been found that over time, as the external additives become fixed into the toner particle surface, for example as a result of impaction through collisions with other toner particles and/or carrier particles, the charge distribution over the surface becomes increasingly non-uniform. This is problematic in that the toner particles may not exhibit uniform charging characteristics, and thus may not develop images of uniform quality. Non-uniform charge distributions on the surface of a particle may also create higher local electric fields on the particles, causing higher levels of electrostatic adhesion to all surfaces in the xerographic engine (for equivalent tribo levels), which in turn leads to decreased levels of development and transfer from the photoreceptor to paper over time.
Moreover, some developers exhibit very high developer triboelectric properties. If developer tribo is too high, at least two adverse effects may be realized. First, high developer tribo makes development more difficult because a higher bias is required to develop the toner onto the photoreceptor. In certain cases, the developed mass per unit area (DMA) is not uniform, causing severe print quality defects. Second, high developer tribo may result in significant accumulation of toner on the wires in the developer housing, resulting in what is known as wire contamination. This can cause visible streaks on the prints.
One approach that has been developed to control the developer tribo is to change the coating on the carrier particles of the developer. For example, addition of a silicone rubber to the surface of the carrier particles has been attempted. This approach has the advantage of being able to tune developer tribo independent of the toner properties. However, subsequent contact of the toner particles with surfaces in the system such as the donor roll, wires, photoreceptor, etc., may still result in an increase in the charge on the toner.
An alternative method may be to adjust the amounts of the external surface additives used on the toner particles. The disadvantage to this approach is that adjustment of the external additive amounts alters other toner properties besides tribo, and the tradeoff is therefore not advantageous.
U.S. Pat. No. 6,511,780 describes a carrier comprised of a mixture of insulating carrier particles and conductive carrier particles in which the conductive carrier particles contain a conductive component. Either of the particles may be provided with a coating of, e.g., polyaniline.
U.S. Pat. No. 6,495,301 describes a toner comprising separate toner particles each of which comprises a fixable core, the core being provided with a conductive surface layer containing a doped electrically conductive polymer and an intermediate layer, particularly a polymer-containing intermediate layer disposed between the surface layer and the core. The intermediate layer is preferably comprised of polymethyl methacrylate, polyvinyl alcohol, polyvinyl pyrrolidone and copolymers of maleic acid and olefins. The doped electrically conductive polymer of the conductive surface layer is preferably derived from at least one monomer selected from the group consisting of thiophene, aniline, pyrrole or derivatives thereof.
In the background section, U.S. Pat. No. 6,495,301 discusses JP 3-100561. This Japanese publication describes obtaining a toner stable in conductivity at low cost by attaching a doped conductive polymer to the surface of each core particle. The conductive polymer, such as an oxidation polymer of aniline, pyrrole, thiophene and derivatives thereof, is attached to the surface of each core particle for composing the toner by immersing the core particles into at least one kind of solvent, such as water or methanol, and stirring them in the presence of at least one kind of monomer, such as aniline or pyrrole, and an oxidant and a dopant, thus permitting an electrophotographic toner satisfying the requirement of stability to be obtained at low cost.